Updates: DST data

exploratory analysis progress of the DST data, master thesis Lotte Pohl, 16.2.2023

where we left off

6 out of 8 recovered tags stopped recording 13-38 days after tagging, i.e. the animal died.

tag_serial_number release_date_time detected sex life_stage length1 length1_unit weight weight_unit capture_depth recapture_date_time animal_id tag_type scientific_name release_latitude release_longitude
1293322 2018-07-19 09:00:00 no f unknown 80 cm NA NA 3-20m 2019-09-29 3175 acoustic-archival Mustelus asterias 51.61002 3.649600
1293319 2018-07-19 12:00:00 yes f unknown 73 cm NA NA 3-20m 2018-08-21 3178 acoustic-archival Mustelus asterias 51.61177 3.649833
1293295 2018-07-19 13:00:00 yes m adult 78 cm NA NA 3-20m 2018-09-27 3182 acoustic-archival Mustelus asterias 51.61250 3.653783
1293304 2019-07-11 10:25:00 no f mature 72 cm 1.35 kg NA NA 5067 acoustic-archival Mustelus asterias 51.61502 3.657802
1293310 2019-07-11 12:20:00 no m mature 72 cm 1.40 kg NA 2019-09-03 5069 acoustic-archival Mustelus asterias 51.61822 3.663183
1293312 2019-07-12 08:15:00 no f unknown 91 cm 2.80 kg NA 2019-08-29 5218 acoustic-archival Mustelus asterias 51.61058 3.656550

Looking at the 6 tracks in more detail, it strikes that 3 sharks swam to the wind farms while 3 sharks stayed very close to the release location, namely tag 304 (female, 13 days of liberty), tag 310 (male, 37 days of liberty) and tag 312 (females, 32 days of liberty). Those 3 sharks were released in 2019.

depth and temperature profiles

This shark (male) swam out to the OWF.

This shark (female) stayed in the Oosterscheldt.

This shark (male) stayed in the Oosterscheldt.

This shark (female) stayed in the Oosterscheldt.

This shark (female) swam out to the OWF.

This shark (female) swam out to the OWF.

depth and temp profiles of long term DST data

These are the profiles of the 2 tags that recorded for over a year.

This shark (female) swam south into the English Channel.

This shark (male) swam north into the Southern North Sea.

what I plan to do now

  • I would like to segment the vertical data logs into behavioural patterns. This was done by Heerah et al., 2017 (https://doi.org/10.1186/s40462-017-0111-3). I spent a day with it already, but it is not trivial to format the code to the M. asterias DST data. To correctly do this, I would need the help of someone that has already done this. Jolien supervised a thesis in 2020 (Camille Boileau-Locas), that did that as well, but I know she has a lot to do right now. Mathieu Woillez also co-authored the paper by Karine Heerah, so I could contact him as well, potentially. What do you suggest?

  • The method of Heerah et al., 2017 uses STFT, a modified version of FFT. I was thinking that I maybe at first do a regular FFT to look at the periodic patterns of the signals.

  • Griffiths et al., 2020 (https://doi.org/10.1371/journal.pone.0239480) did not use any fancy/complex Hidden Markov Models like Heerah but they calculated statistics such as the time spent at certain depth bins, vertical speed, seabed proximity, or vertical movement behvaiour (based on a Wilcoxon test).

  • I am unsure right now what analyses could best shed light on behavioural patterns of the sharks. What are your suggestions?